Electronic toothbrush and electronic brush

ABSTRACT

An electronic toothbrush comprising: a brush head portion having a bristle portion, to be inserted into an oral cavity, for washing teeth; and a holder portion to be exposed outside the oral cavity, wherein TiO z  which is an n-type semiconductor is provided so as to receive external light; and the n-type semiconductor is connected to a negative pole of a solar battery and an electrical potential is superimposed on the n-type semiconductor.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an electronic toothbrush and anelectronic brush, and more specifically to an electronic toothbrush andan electronic brush using a photocatalytic reaction of an n-typesemiconductor.

[0003] 2. Description of the Related Art

[0004] As a method for preventing intraoral diseases such as dentalcaries or alveolar pyorrhea, application of a fluoride on the toothsurface or use of a dentifrice containing a fluoride has beenconventionally practiced in order to further improve the preventioneffect as compared to simply brushing the tooth surface with atoothbrush bearing a dentifrice adhered thereon. However, questionsremains as to the effect of these methods because an fluorine ion isinferior in permeability with respect to pulp tissue, and hence, inorder to improve the effect of the fluorine ion, a method has beensuggested that permeability of a fluorine ion is improved by increasingan electric potential by the action of an external power supply such asbattery, domestic power supply and the like.

[0005] However, also this method is not desirable because it has aproblem that metal ions associated with generation of an electriccurrent will flow out because a metal which is a conductor is used forthe toothbrush portion, and in addition, the electric current,electromagnetic waves, or electric fields can have detrimental effectson a human body when used for a long time.

[0006] In view of the above, the inventors of the present inventioninvented an electronic toothbrush utilizing a photocatalytic reaction ofTiO₂ which is an n-type semiconductor, which does not cause such aproblem (Japanese Unexamined Patent Publication JP-A 58-41549 (SHO-58,1983). TiO₂ is a compound that generates a photoelectron voltage evenunder the irradiation condition by relatively weak light, and wheninserted into the oral cavity, generates OH radicals from the moisturesuch as saliva and elevates the pH in the oral cavity to accomplishneutralization, thereby decreasing the activity of etiologirc bacteriaof dental caries, as well as decomposing dental plaque.

[0007] However, in the case where only the photocatalytic reaction ofTiO₂ is used, the method of decreasing the activity of etiologicbacteria.of dental caries having high activity in an acidic atmospherewill accomplish a predetermined effect as it is, however it inevitablyrequires a certain time before it exerts the effect. In other words, thedirect reason of generation of dental caries is that lactic acid whichis generated at the time when the etiologic bacteria of dental cariesferment saburra attacks hard tissue of a tooth, and there is a problemthat the lactic acid is continuously generated until the activity of theetiologic bacteria of dental caries is decreased.

[0008] The inventors of the present invention made a thorough study forenabling effective decomposition of generated lactic acid, and foundthat effective decomposition of lactic acid can be accomplished byproviding an electric potential of more than or equal to a predeterminedvalue at the time of using the photocatalytic reaction of then-typesemiconductor, and that such an effect acts not only on decomposition ofthe lactic acid but also on decomposition of organic matters.

SUMMARY OF THE INVENTION

[0009] In view of the above problems, it is an object of the inventionto provide an electronic toothbrush which, by using a photocatalyticreaction of the n-type semiconductor, not only decreases the activity ofetiologic bacteria of dental caries but also improves decomposition ofgenerated lactic acid, thereby preventing dental caries moreeffectively, and to provide an electronic brush which can wash each partof a body more effectively than the case where washing is conductedsimply by using soap water, by decomposing organic waste such as dirtgenerated at each part of the body.

[0010] The aforementioned object is accomplished by the inventionaccording to each aspect. That is, an electronic toothbrush according tothe present invention is featured by comprising:

[0011] a brush head portion having a bristle portion, to be insertedinto an oral cavity, for brushing teeth;

[0012] a holder portion to be exposed outside the oral cavity;

[0013] an n-type semiconductor which is formed of TiO₂ and receivesexternal light; and

[0014] a battery which is a solar battery having an output of more than0.5 V and less than3.0V, connected only to the n-type semiconductor suchthat the n-type semiconductor is connected to a negative pole of thesolar battery, and supterimposes an electrical potential on the n-typesemiconductor in order to synergically enhance a photocatalytic effectof the n-type semiconductor.

[0015] According to the present configuration, owing to thephotocatalytic action of the n-type semiconductor, in the case where thetoothbrush is inserted into an oral cavity, in addition to the fact thatOH radicals generated by decomposition of moisture such as salivaincrease the pH within the oral cavity to neutralize the same, therebydecreasing the activity of etiologic bacteria of dental caries, the OHradicals reliably and rapidly decompose lactic acid generated by lacticfermentation of foods by bacteria, so that dental caries can beprevented from occurring. In other words, in contrast to the case whereonly the photocatalytic action of n-type semiconductor effected byexternal light is employed (e.g. fluorescent lamp in a washroom), bysuperimposing the electric potential of the battery, an energy levelrequired for decomposing lactic acid and water can be achieved, so thatthe photocatalytic effect of the n-type semiconductor can be improvedsynergistically. As a consequence, it is possible to improve theefficiency of generation of OH radical while reliably improving the pHby toothbrushing operation. Additionally, in the case of practicallyperforming toothbrushing operation in a washroom and the like, evenunder the condition that light irradiation is weak because illuminationof lighting equipment such as fluorescent lamp in the washroom is low,since the battery which makes the electric potential of the n-typesemiconductor more than or equal to a predetermined value is provided, adesired effect can be stably achieved. As a result, according to thepresent invention, there can be provided an electronic toothbrush thatcan prevent intraoral diseases such as dental caries more effectively.

[0016] Furthermore, since the n-type semiconductor is formed of TiO₂ andthe output of the battery is more than 0.5 V and less than 3.0 V, thefollowing effect is brought about.

[0017] Specifically, TiO₂ is effective for improving decomposition oflactic acid or increasing the pH because it exhibits a particularlylarge photocatalytic effect among n-type semiconductors, and theelectrical potential required for causing a photocatalytic action ismaintained more than or equal to the predetermined value, and thecurrent flowing into a human body via a hand is kept extremely weak toproduce no adverse effect on the human body, which is advantageous. Inother words, when the output of the battery is less than or equal to 0.5V, decomposition of lactic acid is insufficient, whereas when the outputof the battery is more than or equal to 3.0 V, although decomposition oflactic acid is promoted, the current flowing into a human body isincreased to cause discomfort when the toothbrush is held by a wet hand,and thus such ranges are not preferable. More preferably, the output ofthe battery is not less than 1.0 V and less than 3.0 V.

[0018] In the case where TiO₂issued as the n-type semiconductor, thereaction formula for decomposing lactic acid into water and carbondioxide by photocatalytic action is as follows:

[0019] wherein “p⁺” represents a positive hole, “e⁻” represents anelectron and “+OH” represents an OH radical.

[0020] Since the present invention employs a solar battery, thefollowing effects are brought about.

[0021] (a) Since the battery is charged all the time duringtoothbrushing with the toothbrush under irradiation of a fluorescentlamp in a washroom or the like, or in a well-lighted place wheresunlight streams, the photocatalytic action of the n-type semiconductoris not reduced even as operating time goes on, so that the effect of thepresent invention that generation efficiency of OH radicals is improvedto reliably increase the pH is not reduced at all.

[0022] However, in a primary battery, since a gradual voltage dropoccurs as operating time goes on, the voltage drops over time to therebyreduce the effect while a user of the toothbrush is not aware of it. Itis true of a secondary battery, which is rechargeable as in a solarbattery.

[0023] (b) The solar battery, being a thin plate-like, can be wellhoused along an inner surface of the holder portion even at such a placeas the holder portion of the toothbrush, and the holder portion does notneed to be thickened more than necessary. The manufacturing cost,therefore, is not increased.

[0024] (c) The service life of a solar battery is generally 20 years ormore, which is much longer than a primary battery and longer than asecondary battery. A user of the toothbrush does not need change thebattery frequently. Unlike a primary battery, the consumed battery isnot frequently disposed.

[0025] (d) The longer service life of a solar battery can hold down thecost, which is advantageous to a toothbrush which is required to besupplied at low cost. In a rechargeable secondary battery, since abattery charger is required and power consumption for charging isentailed, the cost is higher than that of a solar battery.

[0026] (e) In a solar battery, unlike a primary battery and a secondarybattery, there occurs no liquid leakage when it is deteriorated. Ifliquid leakage occurs, there arises a possibility that a short circuitbetween electrodes occurs, thereby causing heat generation, ignition,disruption or the like. Therefore, it is not preferable to use a primarybattery or a secondary battery for the toothbrush. Accordingly, in thecase of a primary battery, the battery needs to be removed when not usedfor a long time, which is troublesome. A solar battery in which such apossibility never arises is best suited for toothbrush.

[0027] In addition, according to the present invention, since an n-typesemiconductor is connected to a negative pole of a solar battery, aremarkable sterilizing effect is brought about.

[0028] It is preferable that the TiO₂ is an anatase-type crystal.

[0029] The present configuration is effective and advantageous becausesuch a type of TiO₂ has a particularly large photocatalytic effect amongother types of TiO₂. In this context, an anatase-type crystal can beeasily obtained, for example, by the method of heating pure Ti to 1200to 1500° C. for several minutes in an oxidizing atmosphere.

[0030] Furthermore, an electronic brush according to the presentinvention is featured by comprising:

[0031] a brush head portion having a bristle portion;

[0032] an n-type semiconductor which is formed of TiO₂ and receivesexternal light; and

[0033] a battery which is a solar battery having an output of more than0.5 V and less than 3.0 V, connected only to the n-type semiconductorsuch that the n-type semiconductor is connected to a negative pole ofthe solar battery, and superimposes an electrical potential on then-type semiconductor in order to synergically enhance a photocatalyticeffect of the n-type semiconductor.

[0034] According to the present configuration, owing to thephotocatalytic action of the n-type semiconductor, in the case ofwashing each part of a body using soap water and the like, OH radicalsgenerated by decomposition of moisture reliably and rapidly decomposeorganic waste such as dirt on the skin surface, so that higher washingeffect can be achieved compared to the case where only the soap water isused In other words, in contrast to the case where the photocatalyticaction of the n-type semiconductor is caused by only the external light(e.g. fluorescent lamp in a bathroom or washroom), by superimposing theelectric potential of the battery, there can be achieved an energy levelrequired for decomposing organic waste on the skin surface and water, sothat the photocatalytic effect of the n-type semiconductor can beimproved synergistically. As a consequence, the efficiency of generationof OH radicals can be improved by scrubbing operation of skin surface-Additionally, in the case of practically performing washing operation ina bathroom and the like, even under the condition that light irradiationis weak because illumination of lighting equipment is low, and even ifthe lighting equipment is an incandescent lamp rather than a fluorescentlamp, since the battery which makes the electric potential of the n-typesemiconductor more than or equal to a predetermined value is provided, adesired effect can be stably achieved. As a consequence, according tothe present invention, there can be provided an electronic brush capableof washing each part of a body more effectively compared to the casewhere washing is performed with only soap water.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035]FIG. 1 is a schematic partial section view showing one embodimentof an electronic toothbrush according to the present invention;

[0036]FIG. 2 is a section view along the line II-II of FIG. 1 ;

[0037]FIG. 3 is a schematic circuit diagram showing an operating stateof the electronic toothbrush according to the present invention;

[0038]FIG. 4 is a graph showing a sterilizing effect in the ease wherethe electronic toothbrush according to the present invention is used;

[0039]FIG. 5 is a graph showing test results of a lactic aciddecomposition ability of the toothbrush according to the presentinvention;

[0040]FIG. 6 is a graph showing test results of decomposition of alactic acid solution in relation to varied voltage of the solar batteryaccording to the present invention;

[0041]FIG. 7 is a schematic partial section view of one embodiment of anelectronic brush according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0042] Embodiments of the present invention are described in detail withreference to the drawings. FIG. 1 shows a schematic sectional structureof an electronic toothbrush according to the present embodiment(hereinafter, also referred to simply as “toothbrush”). This toothbrush1 comprises a brush head portion 2 in which bristles 2 a are implanted,and a holder portion 3 to be exposed outside an oral cavity. Preferably,these brush head portion 2 and the holder portion 3 can be separatedfrom each other. In other words, when the head portion 2 having thebristles 2 a to be consumed is designed to be replaceable as aconsumable item in case of necessary, in addition to the economicaladvantage, an advantage of reducing the size of the waste compared tothe case where the entire toothbrush is disposed is achieved.

[0043] In the holder portion 3, a TiO₂ rod 4 which is an n-typesemiconductor as well as a solar batter 5 of 1.5 V are incorporated, anda negative pole of this battery 5 and the TiO₂ rod 4 are connected toeach other via a conductive line 6 such as copper wire. At the interfacebetween the brush head portion 2 and the holder portion 3, there isformed a groove 7 by reducing the section partly in order to facilitateirradiation of the external light to the n-type semiconductor. FIG. 3 isa schematic circuit diagram in an operating state of the electronictoothbrush using the solar battery 5. In this case, the negative pole ofthe solar battery is connected to then-type-semiconductor, and a voltageis added to a counter pole as a positive pole, whereby the effect as anoptical semiconductor is increased that much.

[0044] The TiO₂ rod 4 is formed by heating a rod of pure Ti to 1200 to1500° C. in an oxidizing atmosphere for several minutes to thereby forma TiO₂ layer on the surface thereof. TiO₂ of this case is anatase-typecrystalline and thus possesses an especially large photocatalyticcapability. And when the TiO₂ rod 4 receives the external light to giverise to a photocatalytic reaction, the solar battery 5 increases ormaintains the electric potential of TiO₂ which is an n-typesemiconductor.

EXAMPLES Example 1

[0045]FIG. 4 shows results of a test in which the effect of the casewhere a negative pole of a solar battery was connected to an n-typedsemiconductor was investigated.

[0046] The test conditions are as follows.

[0047] As test bacteria, Streptococcus mutans IFO 13955 which isconsidered to be a cause of dental caries was used.

[0048] (i) 4 mL of saline was loaded into a test tube and the testbacteria were inoculated so that a concentration of the test bacteriabecame about 10,000 to 20,000/mL.

[0049] (ii) The solar battery was used and irradiation by a fluorescentlamp (6 W, at a distance of 10 cm) was conducted at normal temperaturesfor 1 to 5 minutes.

[0050] (iii) A viable cell number in 1 mL was measured in a standardagar medium.

[0051] An initial propagation number of bacteria was 1.3×10⁴/mL.

[0052] In the accompanying drawing, (A) shows a case where an n-typesemiconductor was connected to a negative pole of a solar battery(equivalent to the present invention), (B) shows a case where an n-typesemiconductor was connected to a positive pole of a solar battery, and(C) is blank, showing a case where neither n-type semiconductor norsolar battery was used.

[0053] In the case of (A), colonies of Streptococcus mutans decreasedrapidly in number for a short time, which shows remarkable effect wasexerted. Since a toothbrushing behavior is typically performed for ashort time, this result shows the toothbrush according to the presentinvention has high practicality.

Example 2

[0054] Furthermore, the effect of a lactic acid decomposition ability ofthe toothbrush according to the present invention was investigated. FIG.5 shows its test results. This test was conducted in a method ofmeasuring the pH of a lactic acid solution with time.

[0055] A lactic acid solution was blended with 0.3 M potassium sulfatesolution and sodium hydrate was further added thereto so as to adjustthe pH to about 5.7. 10 mL of this solution was loaded into a glassvessel, a structure using sample electrodes (a solar battery 2.0 V isused. negative pole: TiO₂ electrode, positive pole: stainless electrode)was inserted into the solution, and the solution was light-irradiated bya fluorescent lamp of 6 W and subjected to bubbling with an oxygen gasat 1 L/minute. A distance between the vessel and the fluorescent lampwas about 3 cm. A resistor was connected to the sample electrodes tomake predetermined currents (70 μA, 100 μA: equivalent to currentsflowing in a human body at toothbrushing time) flow between theelectrodes. After starting the decomposition, the pH of the lactic acidsolution was measured at intervals of 1 minute in conformity to JISK0101 glass electrode method.

[0056] In either case in which the resistor (A-1: 70 μA, A-2: 100 μA)was connected to the sample electrodes, the pH of the lactic acidsolution rose for a shorter time than in a blank case (C-1: the solutionwith neither n-type semiconductor nor a solar battery used)

Example 3

[0057] A decomposition test of a lactic acid solution was conducted inrelation to varied voltage of a solar battery. The results were shown inFIG. 6. In this test, 50 mL of about 70 ppm lactic acid liquid wasloaded in a flat-bottomed vial (diameter 40×height 75 mm) and electrodesof a negative pole made of an n-type semiconductor with a titanium oxidefilm formed and a positive pole made of stainless steel were insertedinto the resultant lactic acid solution to apply a voltage of 0 to 3 Vbetween these electrodes by a direct current device. The lightirradiation was conducted by a fluorescent lamp of 6 W at a distance of3 cm, and the concentration of lactic acid after a lapse of 24 hours wasmeasured by capillary electrophoresis to investigate the decompositionof lactic acid.

[0058]FIG. 6 shows the decomposition of lactic acid started under a loadvoltage of about 0.5 V and reached saturation at about 2 V. Accordingly,it is clear that the load voltage of the solar battery starts to exert alactic acid decomposion effect at 0.5 V, remarkable effect at 1 V, andsufficient effect at 2 V.

[0059] (Other Embodiments of the Invention)

[0060] (1) In the above embodiment, although an example of an electronictoothbrush using TiO₂ which is an n-type semiconductor has been shown,the TiO₂ which is an n-type semiconductor can be used for an electronicbrush 10 as shown in FIG. 7. More specifically, in this electronic brush10, bristles 10 a are implanted therein on the front side constituting abrush head portion, and a holder portion is formed on the rear side,into which the solar battery 5 is embedded. This solar battery 5 isembedded in a liquid-tight manner. On the front side where the bristles10 a are implanted, TiO₂ similar to that shown in the above embodimentis attached, while a groove 11 which functions as a water passage isformed in the vicinity of the TiO₂, whereby communication of soap waterand the like is enabled. This groove 11 comprises a penetration holeformed toward base portions of the bristles 10 a, and is configured sothat by scrubbing a body with the bristles 10 a, the TiO₂ and thesurface of the body are brought into contact with each other via themoisture, thereby facilitating decomposition and removal of organicmatters such as dirt existing on the surface by the photocatalyticaction of the TiO₂, and also allowing decomposition of the removedorganic matters. Incidentally, the TiO₂ and a negative pole of thebattery are made conductive via the conductor 6 as shown in FIG. 1. Asthe n-type semiconductor, the battery and the conductor, those similarto those used in the above embodiment can be used.

[0061] As the shape of the present electronic brush, various shapesother than that shown in FIG. 7 can be employed as long as theelectronic brush is formed into a shape which enables washing byscrubbing each part of the body with the bristles while the holderportion being held by a hand. Each part of the body to be washed is notparticularly limited, and hence the present electronic brush can beused- as a so-called body brush, hair brush, face brush and the like.

[0062] (2) In the above embodiment, an example in which TiO₂ which is ann-type semiconductor is formed on a Ti rod in layered shape by heatingthe Ti rod, however not being limited to the above configuration, theTiO₂ may be entirely formed by sintering TiO₂ powder so long as a TiO₂layer is formed on the light receiving surface. Also the productionmethod may be such that the TiO₂ layer is generated on the conductivesurface of a pure Ti rod and the like by the CVD method, PVD method andthe like, and that the TiO₂ layer is generated on the surface by anodicoxidation of a pure Ti rod.

[0063] (3) For the electronic toothbrush according to the aboveembodiment, an example is shown such that the groove 7 is formed at theinterface between the brush head portion 2 and the holder portion 3 soas to facilitate irradiation of the external light to TiO₂which is ann-type semiconductor, however, the brush head portion and the holderportion of the toothbrush maybe formed of a light-permeable materialsuch as transparent or translucent acrylic resin, urethane resin, PETresin and the like, thereby providing a structure without the groove. Inaddition, when a biodegradable resin is used as a resin for forming thebrush head portion 2, influence on the environment is diminished even ifthe brush head portion 2 is disposed as a consumable item, which isdesirable.

What is claimed is:
 1. An electronic toothbrush comprising: a brush headportion having a bristle portion, to be inserted into an oral cavity,for brushing teeth; a holder portion to be exposed outside the oralcavity; an n-type semiconductor which is formed of TiO₂ and receivesexternal light; and a battery which is a solar battery having an outputof more than 0.5 V and less than 3.0 V, connected only to the n-typesemiconductor such that the n-type semiconductor is connected to anegative pole of the solar battery, and superimposes an electricalpotential on the n-type semiconductor in order to synergically enhance aphotocatalytic effect of the n-type semiconductor.
 2. The electronictoothbrush according to claim 1, wherein the TiO₂ is an anatase-typecrystal.
 3. An electronic brush comprising; a brush head portion havinga bristle portion; an n-type semiconductor which is formed of TiO₂ andreceives external light; and a battery which is a solar battery havingan output of more than 0.5 V and less than 3.0 V, connected only to then-type semiconductor such that the n-type semiconductor is connected toa negative pole of the solar battery, and superimposes an electricalpotential on the n-type semiconductor in order to synergically enhance aphotocatalytic effect of the n-type semiconductor.
 4. The electronicbrush according to claim 3, wherein the TiO₂ is an anatase-type crystal.